Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.49   5.141%   $216.0542   $216.05   $216.05   $216.10  
  Purchase #2 $101.85   5.604%   $107.5577   $107.56   $107.55   $107.60  
  Purchase #3 $186.90   9.530%   $204.7116   $204.71   $204.70   $204.70  
  Purchase #4 $149.43   8.587%   $162.2616   $162.26   $162.25   $162.30  
  Purchase #5 $46.73   4.555%   $48.8586   $48.86   $48.85   $48.90  
  Purchase #6 $89.96   13.297%   $101.922   $101.92   $101.90   $101.90  
  Purchase #7 $65.87   11.387%   $73.3706   $73.37   $73.35   $73.40  
  7 purchase totals = $846.23       $914.7363   $914.73   $914.65   $914.90